1. Field of the Invention
The present invention relates to a light-emitting material, a light-emitting element containing the light-emitting material, and a display apparatus and an electronic appliance including such a light-emitting element.
2. Description of the Related Art
A light-emitting element containing a light-emitting material is characterized by thinness, lightness in weight, fast response, direct-current low-voltage driving, and so on. The light-emitting element is expected to be applied to a flat panel display of the next generation. Further, a light-emitting device with the light-emitting elements disposed in matrix has a wide viewing angle compared to a conventional liquid crystal display device, so that the light-emitting device is excellent in visibility.
Light emission mechanism of the light-emitting element will be described. When voltage is applied to a light-emitting layer interposed between a pair of electrodes, electrons injected from a cathode and holes injected from an anode are recombined in the light emission center of the light-emitting layer, and molecular excitons are formed. Then, the molecular excitons release light energy in returning to a ground state; consequently, light emission is generated.
A light emission wavelength of the light-emitting element is determined depending on the band gap of a light-emitting molecule contained in the light-emitting element. Thus, light-emitting elements having various kinds of light emission colors can be obtained by devising a structure of the light-emitting molecule. Further, a full color light-emitting device can be manufactured with the use of a red light-emitting element, a blue light-emitting element, and a green light-emitting element.
A red light-emitting element, a green light-emitting element, and a blue light-emitting element are necessary in order to manufacture a full color light-emitting device. However, the development for a highly reliable blue light-emitting material lags behind that of the red light-emitting material or the green light-emitting material. Many studies have been made about the blue light-emitting element in order to solve this problem. (for example, see Patent Document 1: Japanese Published Patent Application No. 2001-335516).